This invention concerns product scanners, particularly scanners to be used in conjunction with product handling apparatus such as cutting or slicing apparatus and especially such apparatus when employed to cut or slice bulk foodstuffs.
In many processes where randomly shaped raw material in bulk form is to be cut into portions, it is desirable to be able to feed to a control system information concerning the geometry and topography of the bulk material before it passes to the cutting step in the process. Such information can enable a control system to calculate where to position the raw material correctly for the cutting operation and to optimise the process to produce the best yield of cut portions from the bulk.
Scanning methods are known whereby product moving along a conveyor is viewed by a TV camera and the information is fed to a computer forming part of a process control system. The accuracy of such systems has not allowed cutting controls signals to allow optimal division of bulk product such as fresh meat, into portions of appropriate size and weight ideal for retailing.
According to one aspect of the present invention, a system is provided in which product traverses an inspection region at a defined position along a conveyor means and at least one distance measuring transducer is mounted for movement around the region in a plane (the inspection plane) generally perpendicular to the movement of the product therethrough, and the distance from the transducer to each of a succession of points on the product surface in the inspection plane is determined by computer means supplied with signals from the transducer and the values are stored and used in a computation to determine at least the shape and/or size of the cross-section of the product in the inspection plane.
Where the product is relatively rigid such as frozen bulk food, it is generally necessary to inspect the surface of the product through 360xc2x0.
Where access to the whole surface is required the inspection plane needs to be at a discontinuity in the conveyor meansxe2x80x94typically a gap between two conveyors.
Where full 360xc2x0 access is not required the conveyor means can if desired extend continuously through the region.
Where the product is not rigid such as fresh meat, the underside of the product will tend to conform to the surface on which it rests. In the case of a conveyor this may be flat or dished to form a trough in line with the conveyor length direction.
Provided the conveyor surface shape is known (and it can be determined if desired by the transducer and computing means without product in the inspection plane) the inspection of the product surface can be restricted to the free surface of the product which if the conveyor is continuous through the inspection station will in any case be fully supported over the whole of its underside which can be assumed to conform to the surface of the conveyor. If (as may be desirable to accommodate cutting blades or saws or simply to render the system able to handle rigid frozen product as well as fresh floppy product) a narrow gap exists in the inspection plane between two conveyors which comprise the conveyor means, one feeding product to the inspection station and the other conveying it away in the same general direction as it is delivered thereto, the underside of the product can still be considered to be the same shape as that of the upper surface of each of the conveyors, thereby obviating the need for the transducer to xe2x80x9cinspectxe2x80x9d the underside of the product where it bridges the narrow gap.
The time required to scan the cross-section can be reduced by using a plurality of transducers equally spaced around the inspection region so that less than 360xc2x0 of movement is needed for the transducers in order for the whole of the surface in the said region to be inspected.
Where less than 360xc2x0 inspection of the surface is required, typically only 180xc2x0 because the underside surface is assumed to be known, the process can be further speeded up by rotating the single transducer or a plurality of equally spaced apart transducers through just sufficient of an angle for all the surface which needs to be inspected to be seen by the transducer or transducers.
According to a preferred feature of the invention, the transducer or transducers are rotated first in one sense and then back in an opposite sense to the same extent, so that flexible cable connections may be made between the transducer or transducers and a stationary computing means.
The shape and/or size value for the product cross-section may be stored for each of a succession of positions of the product relative to the inspection region, to enable the volume of the product to be determined by a further computational step.
Preferably signals are generated when a length of product enters and leaves the inspection region and to this end proximity or movement sensors may be provided at appropriate positions along the conveyor means, or the inspection transducer or transducers and the computation means may be programmed to produce product arrival and product departure signals.
In one embodiment transducers are located at 90xc2x0 intervals around the inspection region, for movement in synchronism and the movement may be continuous or oscillatory, so as to inspect the whole of the surface of product.
Thus for example laser displacement transducers may be mounted at 90xc2x0 intervals around a ring and positioned so that they direct their beams through a gap between two in line conveyors, and the ring may be driven in rotation by a servo motor.
Conveniently the servo motor is controlled by a computer, which conveniently is employed also to perform the computation on the cross-section data gathered from the transducer(s).
Preferably four such transducers are arranged equally spaced around the ring and the output of each of the transducers is logged by the computer means.
Where only a single transducer is employed it is necessary to rotate it around the whole of the arc over which inspection is required, and if full 360xc2x0 inspection is required, the arc must extend around a full 360xc2x0 centered on the product.
If the arcuate movement of the transducer or transducers is fast enough in relation to the linear movement of the product, the locus of the inspection point around the surface of the product is a closed path similar to the line which will be produced if a very thin knife were to have sliced through the product leaving the two cut surfaces abutting. If the product happened to be of a circular cross-section, and the product is stationary or the transducer speed of rotation is very fast relative to the linear speed of the product, the locus of the inspection point will be a closed circle.
If the rotation is not fast enough, the locus of the point will describe a continuous path somewhat in the form of a helix, the cross-sectional shape of which will be determined by that of the product log. Only a true helix will occur in the case of product whose cross-section is circular. The xe2x80x9chelicalxe2x80x9d type of path is that which will normally be obtained.
A true cross-section can be obtained if the movement of the product is intermittent, so as to move relative to the transducer(s) in a series of steps, and where the output of the transducer(s) is only used when the product is stationary, or the transducer(s) is/are switched so as only to be active when the product is stationary.
In a preferred embodiment for use with fresh meat bulk product, three transducers are arranged equidistantly around an arc centred on the inspection region so that it is only necessary for the array to rotate through 60xc2x0 for the entire upper surface of the bulk product to be traversed by the three transducer inspection spots, thereby reducing the advance of the xe2x80x9chelixxe2x80x9d per scan, and allowing either a greater linear speed of the product through the inspection plane or a higher sampling rate of the bulk product cross-section and therefore a more accurate description of each product cross-section to be obtained. By oscillating the array back and forth through 60xc2x0 and scanning during both forward and reverse movements of the transducer array the whole of the upper surface of the product can be scanned by the transducer light spots as it passes through the inspection plane.
An arc containing three transducers typically extends around 120xc2x0 C.
If six transducers were mounted equidistant around a 150xc2x0 arc, the sampling rate, or the linear product speed, can be doubled, since it is only necessary to rotate the array through 30xc2x0 for all the circumference which is to be inspected, to be seen.
Where it is desirable that the transducer or transducers is/are to rotate continuously, slip ring connections may be employed, or one or more low power radio transmitter devices may be associated with the transducer array for transmitting transducer output signals as a modulation of a radio signal to a nearby stationary receiver, from which they are conveyed to a computer means.
Where one transmitter is mounted on an array of two or more transducers, the output of each transducer may be transmitted on a different channel, or time division multiplexing, or any other multiple channel technique may be employed, to transmit the two or more transducer output signals to one or more radio receivers adapted to decode the received signal or signals to allow the distance data to be derived from the received radio signals for input to the computer means.
The conveyor means may also be driven by at least one servo motor which may also be controlled from the computing means in a similar way to the servo motor driving the transducer array, and the or each conveyor servo motor is synchronised to provide reliable transfer of product from one conveyor to the other across any gap. Preferably the computer control also synchronises the transducer scanning servo motor in relation to the conveyor motion.
Sensors may be provided to deliver feedback signals to the computer to indicate actual movement of the conveyor and/or transducer(s), to provide a form of closed loop servo control and to indicate to the computer when product is about to enter or leave the inspection plane or any interruption in either movement occurs.
According to another aspect of the invention there is provided a method of determining the volume of a length of bulk product having a varying cross-section, comprising the steps of linearly moving the product through an inspection plane which extends generally perpendicular to the linear movement of the product by motor-driven conveyor means, moving a distance measuring transducer along an arcuate path in the inspection plane, computing the length of the product by reference to its linear speed past at least one detector which may be the transducer or transducers, and computing the distance from the transducer to each of a succession of points around the product surface in the inspection plane, and computing therefrom the area of the cross-section defined by the said points, and where these do not extend completely around the product cross-section, employing stored data about the shape of the surface supporting the bulk product in, or just upstream or downstream of the inspection plane, to provide a complete set of data by which to compute the cross-sectional shape and/or area, determining the increments of volume of bulk product attributable to each transducer scan by reference to the distance moved by the product before the next scan, and summarising the increments of volume over the whole of the length of the bulk product as it progresses through the inspection plane.
The method also comprises the steps of scanning the conveyor support surface in the inspection plane and storing data relating thereto, when product is absent.
The weight of the bulk product can be computed by employing a mean density value and multiplying volume by mean density, and an example of such a process to which the invention can be applied is one in which a log of fresh meat is to be fed into a cutting machine in which the position and/or angle of each cut determines the size and/or weight and/or volume and/or shape of the severed portions. Using the invention portions of constant weight or constant volume or a particular shape can be cut from any particular lump of meat, and/or the volume/shape/weight may be adjusted so as to produce the optimum number of steaks and end pieces from the bulk.
Other applications lie in the field of grading product, where product is sorted weight, volume, length etc.